This is a little hard to say since the speed of innovation and first-mover advantage has become more important relative to the Christmas rush recently.
Typically, products like MP3 players had most of their sales in November and December. As a result, manufacturing cycles and development cycles dictated that the next best thing was ready for stores by September or October. This causes last year's model to be deeply discounted in the winter and summer months.
With high-tech stuff like this we are now seeing many companies release their products as soon as possible to get a first mover advantage - regardless of the time of year. This may lead to low prices at unexpected times.
In general, however, winter is the best time for a deal on MP3 players.